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SULPHANILIC ACID                          175

drop of benzaldehyde. In a short time the phenylhydrazone of
benzaldehyde will crystallise out.                                                                  I

4. Plienylmethylpyrazolone. Mix together 10 grams dry                   ;

phenylhydrazine hydrochloride*ancl 9 grams acetoacetic ester in a
flask (200 c.c.), add 3 or 4 drops cone, hydrochloric acid and
warm for 10  15 minutes.- A clear reddish solution is obtained,                        , jf

which is poured into water and carefully neutralised with caustic                         (

soda.     The precipitated oil solidifies almost immediately and                        ;',

can be recrystallised from alcohol ; m. p. 127.    Yield 8 grams.                        !

!             CH3.C CH2.CO                                        { ,

j-4-H2O + C2H5OH.
See also the Reactions on pp. 70, and   135, and Appendix,
p. 287.
x':~"                                 /NH2    i
Snlphanilic Acid, C6H4<;
\S03H     4
Gerhardt, Annalen, 1846, 60, 312 ; Buckton, Hofmann,
Annalen, 1856, 100, 163.
25 grms. aniline.
80         cone, sulphuric acid.
The aniline and sulphuric acid are cautiously mixed in a '
round flask (250 c.c.) and heated to 180190 in an oil or metal
bath for four to five hours until a sample dissolved in water
remains clear on the addition of caustic soda in excess and no
aniline separates. The product is poured into cold water, which
precipitates the sulphanilic acid as a grey crystalline mass. ' It
is filtered, washed with a little cold water, recrystallised from
hot water with the addition of a little animal charcoal, and dried
in the air. Yield, 2530 grams.
CCH5NH2 + H2SO4-= NH2.CGH4.S03H 4- H2O.
Properties.  Colourless rhombic plates, containing 2 mols. of
water of crystallisation, which they lose slowly in the air, and
the crystals fall to powder. See Appendix^ p. 289.